CDF test
The CDF test is a test method for determining and assessing the durability of concrete against freeze-thaw attacks when using de- icing agents . The term "CDF" is an abbreviation of the full English title Capillary suction of de-icing solution and freeze thaw test , in German Capillary suction of de-icing solution and freeze-thaw alternation test .
The experiment was developed by the International Association of Testing and Research Laboratories for Building Materials and Structures ( RILEM ).
Background and standardization
The CDF test was published in 1996 when the currently valid generation of European standards for concrete was being worked on and not yet introduced. The CDF test is now part of DIN CEN / TS 12390-9: 2006-08, "Testing hardened concrete - Part 9: Resistance to frost and de-icing salt - weathering". The purpose of the CDF test is to create a practical and meaningful test tool for both manufacturers and users of concretes that are exposed to freeze-thaw cycles and de-icing agents, which can make statements about the actual durability of the concrete. The essence of the test method goes beyond the qualitative description of concrete according to the European standard EN 206-1 through exposure classes and assesses the actual, measurable durability of concrete in each individual case.
Concrete attack by frost with de-icing agent is considered in exposure classes XF2 to XF4 according to EN 206-1. The concretes of these classes have frost-resistant properties due to concrete technological limit values such as a minimum binder content , a maximum permissible water-cement value, a minimum compressive strength and a minimum and maximum value of the air void content. However, the standard does not take into account any quantitatively measurable durability in relation to freeze-thaw cycles under the influence of thawing agents. Factors such as the frost resistance of the aggregate , the use and effect of an air-entraining agent , the type and nature of frost exposure are not taken into account, which in certain circumstances can lead to damage to the concrete and the structure itself despite compliance with the limit values.
Experimental setup and implementation
The CDF test is a destructive test method in which weathering is caused on a test specimen by freeze-thaw cycles under defined conditions . The degree of weathering is quantified with the method and is used to compare different concretes.
Specimen
Cubes with an edge length of 15 cm are produced as test specimens with the concrete formulation to be tested. One of the sides of the cube serves as the test surface, which should have the same surface structure as the future building in order to achieve a realistic result for this building. The concrete is post-treated for 7 days, initially in the formwork, after reaching sufficient strength in a water bath. This is followed by dry storage up to a concrete age of 28 days. A few days before the end of the dry storage, apart from the test surface and the side opposite it, the sides of the test cube are sealed watertight and airtight, e.g. B. with epoxy resin in order to later limit the capillary suction of the de-icing agent solution to the test area.
Thawing agent absorption and freeze-thaw cycle
After the dry storage, the test surface of the test specimen is immersed 5 mm deep in a deicing agent solution at room temperature for 7 days. This test liquid is a three percent sodium chloride solution . This is followed by cleaning the test surface in an ultrasonic bath in order to remove loose components from the surface and not mistakenly attribute them to the subsequent frost attack.
A freeze-thaw cycle of the CDF test lasts 12 hours and includes cooling from room temperature +20 ° C to −20 ° C in exactly 4 hours, holding it at −20 ° C for three hours and heating the sample back to +20 ° C in another 4 hours. The temperature of +20 ° C is maintained for one hour. The temperature deviation, measured at the bottom of a test container, may only be ± 0.5 K during the phase at −20 ° C. A deviation of ± 1 K is permitted for all other times of the test cycle. 28 such cycles are run to complete the test.
Result and evaluation
The dry mass of the weathered concrete pieces is used to determine the freeze-thaw cycle resistance. A limit value or an acceptance criterion in the CDF method for the maximum permissible weathering does not exist in either a German or a European standard. However, it is possible to evaluate concretes for hydraulic structures or for exposure class XF4 using the CDF method and three percent sodium chloride solution based on the acceptance criterion for weathering of 1500 g / m² after 28 freeze-thaw cycles on test specimens that were produced in the laboratory and whose test surfaces were peeled against Teflon.
Application of the test procedure
The CDF test is used in several European countries where the test is prescribed by building authorities. In Germany there are corresponding instructions u. a. from the State Office for Building and Transport of the Free State of Thuringia and from the Federal Institute for Hydraulic Engineering . The CDF test, on the other hand, is not an official test procedure in Austria and Italy. There, other standards apply and also other, nationally different weathering limit values.
Further procedures
Further frost test methods for concrete are the plate test method and the cube test method, which, like the CDF test, are described in DIN CEN / TS 12390-9: 2006-08. Indirect test methods for determining the durability of concrete against frost and thawing agent stress are counting the air pores and determining the distance factor using thin-section specimens under a light microscope.
The CIF test is used if the resistance of concrete is to be tested under alternating freeze-thaw conditions without de-icing agents . In this experiment, the de-icing agent solution is replaced by water.
Web links
- CDF test specification (German translation): "CDF test - test method for the freeze-thaw resistance of concrete - test with de-icing agent solution (CDF)". (PDF; 320 kB) University of Duisburg-Essen, accessed on August 18, 2013 .
Individual evidence
- ↑ a b Service instructions for the frost and de-icing salt resistance of concrete. (PDF; 12.7 MB) State Office for Building and Transport of the Free State of Thuringia, May 13, 2008, accessed on August 18, 2013 .
- ↑ a b c CDF test specification (German translation): "CDF test - test method for the freeze-thaw resistance of concrete - test with de-icing agent solution (CDF)". (PDF; 320 kB) University of Duisburg-Essen, accessed on August 18, 2013 .
- ↑ CDF test for testing the frost resistance of concrete. Association of German Cement Works, accessed on August 22, 2014 .
- ↑ BAW leaflet: Frost testing of concrete. (PDF; 383 kB) (No longer available online.) Federal Institute for Hydraulic Engineering, 2012, archived from the original on January 18, 2015 ; Retrieved August 18, 2013 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
